1. Field of the Invention
The present invention relates to a lens driving apparatus for moving a lens, specifically a focus lens for adjusting focus, along an optical axis; and a lens barrel comprising such lens driving apparatus.
2. Related Background Art
Japanese Patent Application Laid-Open No. 2000-275494 discloses a lens driving mechanism for moving a lens along its optical axis. This lens driving mechanism comprises a motor having a lead screw extending along the optical axis as a rotary driving shaft; a bridge having a thread hole in mesh with a threaded part of the lead screw; and a lens holding frame, connected to the bridge, for holding the lens. As the lead screw rotates, the bridge moves along the optical axis, whereby the lens holding frame can be moved along the optical axis. The lens holding frame is slidably attached to a guide shaft extending along the optical axis, whereby the lens holding frame is guided so as to move along the optical axis.
Also, Japanese Patent Application Laid-Open No. Hei7-43583 discloses a lens driving apparatus for moving a lens along its optical axis. This lens driving apparatus comprises a motor having a lead screw extending along the optical axis as a rotary driving shaft; a nut in mesh with a threaded part of the lead screw; and a lens holding frame, formed with an accommodating part for accommodating the nut, for holding the lens. As the lead screw rotates, the nut moves along the optical axis, whereby the lens holding frame moves with the nut along the optical axis.
Further, Japanese Patent Application Laid-Open No. 2000-194045 discloses a lens barrel having a plurality of lens cylinders and enabling them to expand/collapse in a multistage fashion between an accommodating position and a use starting position. Disposed within the lens barrel is a lens driving apparatus for moving the lens along its optical axis.
In such a conventional lens driving mechanism, however, the bridge or nut in mesh with the lead screw and the lens holding frame slidably attached to the guide shaft are connected to each other or accommodated together, thereby substantially being integrated with each other. Therefore, when the axis of the lead screw shifts from the axis of the guide shaft, snagging may occur, thereby generating such inconveniences as malfunctioning, deformation in each member, and shifting of the optical axis. Further, it is problematic in that xe2x80x9crattlingxe2x80x9d is likely to occur due to the backlash in meshing parts.
Also, in the conventional lens barrels mentioned above, electric control is carried out such that the lens of the lens driving apparatus do not come into contact with other members when the lens cylinders are collapsed to its accommodating positions. Therefore, they are problematic in that the apparatus configuration is complicated, and are inconvenient in that an operation for accommodating them takes time.
Hence, it is an object of the present invention to provide a lens driving apparatus which suppresses the occurrence of inconveniences such as malfunctioning, deformation of members, and shifting of the optical axis.
It is another object of the present invention to provide a lens barrel in which accommodating operation can be carried out without electric control while preventing the lens from coming into contact with other members.
For achieving the above-mentioned object, the lens driving apparatus in accordance with the present invention is a lens driving apparatus for moving a lens along an optical axis, the lens driving apparatus comprising a lead screw rotated by a driving source; a nut plate formed with a threaded part meshing with a threaded part of the lead screw and adapted to move along the optical axis as the lead screw rotates; a lens holding frame for holding the lens, provided so as to abut against the nut plate while being slidable with respect to a guide shaft extending along the optical axis; and urging means for urging the lens holding frame against the nut plate.
According to such a lens driving apparatus, the lens holding frame abuts against the nut plate while being urged against the nut plate by the urging means, thereby moving along the optical axis as the nut plate moves.
Since the urging action caused by the urging means is transmitted to the nut plate byway of the lens holding frame, the nut plate moves by the amount of backlash with respect to the lead screw, thereby being biased.
Preferably, the threaded part of the nut is less than one pitch. As a consequence, even when an error exists in each pitch width of the lead screw, friction/load is restrained from occurring as the lead screw rotates.
Also, forming the threaded part into less than one pitch simplifies the die-cutting step when molding the nut plate.
Further, it contributes to making the whole apparatus smaller.
Preferably, the lens holding frame abuts against the nut plate about the lead screw. When the nut plate meshes with the lead screw, xe2x80x9crattlingxe2x80x9d occurs due to the backlash therebetween. When the lens holding frame and the nut plate are thus designed so as to abut against each other about the lead screw such that the movement of the nut plate is transmitted to the lens holding frame by way of the abutting part, the influence of xe2x80x9crattlingxe2x80x9d can be reduced.
Preferably, the nut plate has a through hole through which the guide shaft penetrates. This can prevent the nut plate from rotating together with the lead screw as the lead screw rotates.
Preferably, the through hole is a slot. Such structure absorbs the deviation between the axis of the lead screw and the axis of the guide shaft, thereby preventing malfunctions from occurring due to axial misalignment.
The lens may be a focus lens for adjusting focus in a taking optical system.
The lens barrel in accordance with the present invention comprises moving means for moving the above-mentioned lens driving apparatus to an accommodating position along the optical axis; and separating means for separating the lens holding frame from the nut plate at a predetermined position by abutting against the lens holding frame when the lens driving apparatus is moved by the moving means to the accommodating position.
In such a lens barrel, in an accommodating operation of the lens driving apparatus, the separating means separates the lens holding frame from the nut plate by abutting against the lens holding frame, so that the lens can be stopped at a predetermined position, whereby collisions with other members can be prevented from occurring.
Examples of separating means include a boss, disposed at the accommodating position of the lens barrel, projecting by a predetermined amount along the optical axis; and a boss, disposed in the lens holding frame, projecting by a predetermined amount along the optical axis.